Display device having touch panel

ABSTRACT

A display device is provided and includes pixels and common electrodes overlapping the pixels; gate lines connected to pixels in row; source lines connected to pixels in column; source amplifiers; and a gate drive circuit configured to supply at least one first pulse to the gate lines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/658,815, filed on Jul. 25, 2017, which application is based upon andclaims the benefit of priority from Japanese Patent Application No.2016-145603, filed Jul. 25, 2016, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device with atouch detecting function, and a method of driving the display device.

BACKGROUND

In recent years, a portable electronic device such as a smart phone or atablet has a display device with a touch sensor. The touch sensordetects contact or close proximity of a conductive material (hereafter“contact” and “close proximity” is generically called “touch”). Theconductive material includes a finger, a stylus, and so forth. Such anelectronic device displays on a screen a menu image including manyicons, for example, and determines which icon is touched in order torecognize which action the electronic device should take. Consequently,a user can operate an electronic device, without using such an inputdevice as a keyboard, a mouse, or a keypad.

A touch sensing system includes an optical type system, a resistancetype system, a capacitance type system, and others. Among them, thecapacitance type system is widely used since it is comparatively simplein structure and little in energy consumption. A touch sensor employinga capacitance type system detects a touch using a fact that an electrodewill change in its capacitance when an electric conductor approaches theelectrode (i.e., an electrode will increase in capacitance when anelectric conductor approaches the electrode).

It is possible to attach a touch panel with such a touch sensor on ascreen of a display device. In recent years, however, a touch panel isbuilt into a display device in many cases. With the progress of makingthinner a display device with a touch panel, electrodes of a touchsensor is closer to various wirings for driving the display device todisplay an image or the wirings is much closer to one another. As aresult, parasitic capacitance may be connected among them. If parasiticcapacitance is connected between a driving electrode and a wiring in acapacitance type touch sensor, a drive signal will deteriorate inwaveform and is delayed in transmission, whereby touch detectiondeteriorates in accuracy or detection time is long. In this way, acapacitance type touch sensor is easily affected by parasiticcapacitance.

SUMMARY

The present disclosure relates generally to a display device and amethod of driving a display device.

In an embodiment, a display device is provided. The display deviceincludes a pixel array comprising pixels two dimensionally arranged inrows and columns; common electrodes over the pixel array for capacitancetype touch detection; a common electrode driver configured to supply avoltage for display to the common electrodes during a display period anda drive signal for touch detection to the common electrodes during atouch detection period; source lines connected to the columns of thepixels in the pixel array; a source amplifier configured to supply animage signal to the source lines; gate lines connected to the rows ofthe pixels in the pixel array; a gate driver configured to successivelysupply a scanning signal to the gate lines during a display period, andsupply a signal in the same phase as the drive signal to the gate linesduring a touch detection period; and first switches connected betweenthe source lines and the common electrodes and configured to connect thesource lines and the common electrodes during a touch detection period.

In another embodiment, a method of driving a display device is provided.The method includes a pixel array comprising pixels two dimensionallyarranged in rows and columns; common electrodes over the pixel array forcapacitance type touch detection; a common electrode driver connected tothe common electrodes; source lines connected to the columns of thepixels in the pixel array; a source amplifier connected to the sourcelines; gate lines connected to the rows of the pixels in the pixelarray; a gate driver connected to the gate lines; and switches connectedbetween the source lines and the common electrodes, the methodcomprising: supplying, by the common electrode driver, a voltage fordisplay to the common electrodes during a display period; supplying, bythe common electrode driver, a drive signal for touch detection during atouch detection period; supplying, by the source amplifier, an imagesignal to the source lines; successively supplying, by the gate driver,a scanning signal to the respective gate lines during a display period;successively supplying, by the gate driver, a signal in the same phaseas the drive signal to the gate lines during a touch detection period;and connecting, by the switch, the source lines and the commonelectrodes each other during a touch detection period.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating an exemplarystructure of a display device with a touch detecting function accordingto an embodiment.

FIG. 2 is a circuit diagram illustrating an exemplary pixel array.

FIG. 3 is a sectional view schematically illustrating an exemplarystructure of the display device.

FIG. 4 is an exemplary view illustrating a principle of touch detectionin a mutual sensing system.

FIG. 5 is an exemplary view illustrating how display periods and touchdetection periods are arranged in one frame period.

FIG. 6A is an exemplary view illustrating a principle of touch detectionin a self sensing system.

FIG. 6B is an exemplary view illustrating a principle of touch detectionin a self sensing system.

FIG. 7A is an exemplary view illustrating a principle of touch detectionin a self sensing system.

FIG. 7B is an exemplary view illustrating a principle of touch detectionin a self sensing system.

FIG. 8A is an exemplary view illustrating a touch detection circuit of aself sensing system.

FIG. 8B is an exemplary view illustrating a touch detection circuit of aself sensing system.

FIG. 9 is an exemplary graph illustrating a relation between capacitanceCx and voltage Vx and a relation between capacitance Cc and voltage Vc,illustrated in FIGS. 8A and 8B.

FIG. 10 is an exemplary view illustrating how display periods and touchdetection periods are arranged during one frame period in a simultaneousdrive self sensing system.

FIG. 11 is an exemplary block diagram schematically illustrating thedisplay device.

FIG. 12 is an exemplary block diagram illustrating a display controller.

FIG. 13 is an exemplary block diagram illustrating a portion in a panelcontrol signal generator, the portion relating to a guard drive of thegate lines.

FIG. 14 shows an exemplary timing chart illustrating the guard drive ofthe gate lines.

FIG. 15 is an exemplary circuit diagram illustrating a portion in thepanel control signal generator, the portion relating to a generation ofa select control signal supplied to a select switch in the panel controlsignal generator.

FIG. 16 shows an exemplary timing chart illustrating a selectionoperation of the select switch.

FIG. 17 is an exemplary circuit diagram illustrating a select controlsignal generator of a select switch in the panel control signalgenerator according to a second embodiment.

FIG. 18 shows an exemplary timing chart illustrating a guard drive for aselect signal line of the select switch according to the secondembodiment.

FIG. 19 is an exemplary circuit diagram illustrating a select controlsignal generator for a select switch in the panel control signalgenerator according to a third embodiment.

FIG. 20 shows an exemplary timing chart illustrating a guard drive for aselect signal line in the select switch according to the thirdembodiment.

FIG. 21A is an exemplary view explaining the guard drive for an outputof a source amplifier according to a fourth embodiment.

FIG. 21B is an exemplary view explaining the guard drive for the outputof the source amplifier according to the fourth embodiment.

FIG. 21C is an exemplary view explaining the guard drive for the outputof the source amplifier according to the fourth embodiment.

FIG. 21D is an exemplary view explaining the guard drive for the outputof the source amplifier according to the fourth embodiment.

FIG. 22 shows an exemplary timing chart illustrating the guard drive forthe output of the source amplifier according to the fourth embodiment.

FIG. 23 is an exemplary view explaining the guard drive for the outputof the source amplifier according to a fifth embodiment.

FIG. 24 is an exemplary view explaining the guard drive for the outputof the source amplifier according to a sixth embodiment.

FIG. 25 shows an exemplary timing chart illustrating the guard drive forthe output of the source amplifier according to the sixth embodiment.

FIG. 26 is an exemplary view explaining the guard drive according to aseventh embodiment.

FIG. 27 is an exemplary block diagram illustrating a portion relating tothe guard drive for a gate line in the panel control signal generatoraccording to an eighth embodiment.

FIG. 28 is an exemplary diagram indicative of a signal waveform of apower source line according to the eighth embodiment.

DETAILED DESCRIPTION

Embodiments will be described hereinafter with reference to theaccompanying drawings.

In general, according to one embodiment, a display device comprises apixel array comprising pixels two dimensionally arranged in rows andcolumns; common electrodes over the pixel array for capacitance typetouch detection; a common electrode driver configured to supply avoltage for display to the common electrodes during a display period anda drive signal for touch detection to the common electrodes during atouch detection period; source lines connected to the columns of thepixels in the pixel array; a source amplifier configured to supply animage signal to the source lines; gate lines connected to the rows ofthe pixels in the pixel array; a gate driver configured to successivelysupply a scanning signal to the gate lines during a display period, andsupply a signal in the same phase as the drive signal to the gate linesduring a touch detection period; and first switches connected betweenthe source lines and the common electrodes and configured to connect thesource lines and the common electrodes during a touch detection period.

The disclosure is merely an example and is not limited by contentsdescribed in the embodiments described below. Modification which iseasily conceivable by a person of ordinary skill in the art comes withinthe scope of the disclosure as a matter of course. In order to make thedescription clearer, the sizes, shapes and the like of the respectiveparts may be changed and illustrated schematically in the drawings ascompared with those in an accurate representation. Constituent elementscorresponding to each other in a plurality of drawings are denoted bylike reference numerals and their detailed descriptions may be omittedunless necessary.

First Embodiment General Structure

FIG. 1 is a perspective view schematically illustrating an exemplaryoverall structure of a display device with a touch detecting functionaccording to an embodiment. The display device includes a display panelwith a touch detection mechanism, a drive circuit and a control circuitfor the display panel. The display panel includes a display panel usinga liquid crystal and a display panel using organic electroluminescence.In the following, a display panel using a liquid crystal will beexplained, as an example. A liquid crystal display panel includes apixel substrate in which thin film transistor (TFT) pixels are formed.

“Touch detection” means to detect that an object such as a finger or astylus not only touches but also is brought in close proximity to adisplay panel. An “integral type” means that that a touch sensor isbuilt in a display panel and does not mean that a touch sensor isexternally attached to a display panel. “Built in” includes an “in cell”type and an “on cell” type. In an “in cell” type, touch sensor isprovided on a pixel substrate. In an “on cell” type, a touch sensor isprovided between a polarizing plate and a glass substrate having a colorfilter. An “in cell” type touch sensor will be explained as anembodiment. However, an “on cell” type is also applicable to theembodiment.

A display panel includes a first transparent substrate (hereinafter,called a first substrate) 12 of glass, resin, or the like; a secondtransparent substrate (hereinafter, called a second substrate) 14 ofglass, resin, or the like and facing the first substrate 12. A liquidcrystal layer (not illustrated) is between the first substrate 12 andthe second substrate 14. The first substrate 12 may be called a pixelsubstrate because pixels are formed in a matrix shape, as illustrated inFIG. 2. The second substrate 14 may be called a counter substrate. Thedisplay panel is observed from a side where the second substrate 14 islocated. Therefore, the second substrate 14 may be called an uppersubstrate, and the first substrate 12 may be called a lower substrate.

The display panel is formed like a rectangular flat board having ashorter side extending along X axis and a longer side extending along Yaxis. The size of the first substrate 12 and the size of the secondsubstrate 14 are the same in the shorter side but different in thelonger side. The first substrate 12 is longer than the second substrate14 in the loner side. Therefore, if one of the shorter sides of thefirst substrate 12 and one of the shorter sides of the second substrate14 are aligned, the other of the shorter sides of the first substrate 12locates outside of the second substrate 14. A display controller 16 fordriving the display panel to display an image is mounted on an extensionof the first substrate 12 that projects from the second substrate 14along Y axis. It is possible to make the display controller 16 as anintegrated circuit. If the display controller 16 is made as anintegrated circuit, it may be called a display controller IC.

A central part of the display panel constitutes a display region (or anactive area) in which a TFT pixel array 18 is arranged. A touch panel 20is integrally formed with the pixel array 18. The touch panel 20includes driving electrodes 22-1, 22-2, . . . , (generically named 22),as illustrated in FIG. 4 etc., for touch detection on the firstsubstrate 12 and detecting electrodes 24 for touch detection on thesecond substrate 14. The driving electrode 22 for touch detection alsoserves as a driving electrode for display. Thus, the driving electrode22 hereinafter sometimes referred to as a common electrode. Thedetecting electrode 24 and the common electrode 22 are formed oftransparent electrode materials, such as indium tin oxide (ITO) orindium zinc oxide (IZO), so that trouble may not occur to a displayedimage.

A capacitance type touch sensor is classified into a mutual sensing(mutual capacitance) system and a self sensing (self capacitance)system. A pair of electrodes with a dielectric between them is providedin either system. In a mutual sensing system, when a driving pulse issupplied to one of a pair of the electrodes (also called a commonelectrode), an electric field will occur between the common electrodeand the other of a pair of the electrodes (also called a detectingelectrode). If an electric conductor, such as a user's finger, touches atouch panel, an electric field will also occur between the electricconductor and the common electrode because the electric field havingbeen generated between the common electrode and the detecting electrodewill reduce. As a result, electric charges between the common electrodeand the detecting electrode will reduce. A touch position may bedetected by detecting reduction of the amount of electric chargesthrough the detecting electrode.

A self sensing system only uses either a common electrode or a detectingelectrode. For example, if a common electrode is used, parasiticcapacitance exists between the common electrode and a ground voltage.When an electric conductor touches the vicinity of a common electrode,an electric field occurs between the common electrode and the electricconductor. When the electric conductor approaches, the capacitanceconnected between the common electrode and the ground voltage increases.The amount of electric charges accumulated between the common electrodeand the ground voltage changes. A touch position is detected bydetecting change of the amount of electric charges through the commonelectrode. A touch sensor employing a self sensing system will beexplained as a first embodiment, but a touch sensor employing a mutualsensing system may be applied to the first embodiment.

A display device externally has a host device 26. The display device isconnected through two flexible printed circuit boards (FPC) 28 and 32 tothe host device 26. The host device 26 is connected through the flexibleprinted circuit board 28 to the first substrate 12 and the secondsubstrate 14. A touch sensing device 34 controlling the touch panel 20is placed on the flexible printed circuit board 28. It is possible tomake the touch sensing device 34 into an integrated circuit (IC). If thetouch sensing device 34 is made into an IC, it may be called a touchcontroller IC.

The display controller 16 and the touch sensing device 34 arecooperatively synchronized with each other in operation, and areelectrically connected with each other using, for instance, a timingpulse or the like. It is possible to integrate the display controller 16and the touch sensing device 34 into a single integrated circuit chiprather than two respective integrated circuit chips.

The first substrate 12 has a back side (i.e., a back side of the displaypanel) where a back light unit 36 is placed as a lighting system forlighting up the display panel. The host device 26 is connected throughthe flexible printed circuit board 32 to the back light unit 36. Varioustypes of back light units may be used as the back light unit 36. A lightemitting diode (LED) or cold cathode fluorescence lamp (CCFL) may beused as a light source. Moreover, it is possible to use a lightingsystem having a light guide plate, placed at the back side of thedisplay panel, and LED or CCFL placed beside the light guide plate.Alternatively, it is also possible to use a point light source whereinlight emitting elements two dimensionally arranged over the back side ofthe display panel. A lighting system is not limited to a back lightsystem. It is possible to use a front light system placed at a displaysurface side of the display panel. Furthermore, if a display device is areflection type display device, or if a display panel uses organicelectroluminescence, a lighting system is unnecessary.

A display device has a rechargeable battery, a power source circuit,etc., although not shown in FIG. 1.

Pixel Array

FIG. 2 is a circuit diagram indicative of the pixel array 18. The firstsubstrate 12 has a central part where the pixel array 18 is formed. Thepixel array 18 includes pixels 40 arranged in rows and columns to form amatrix (for example, 1080×1920). Each of the pixels 40 is made of a redsub pixel 42 _(R), a green sub pixel 42 _(G) and a blue sub pixel 42_(B) (42 _(R), 42 _(G) and 42 _(B) may be generically named 42). Threecolors other than red, green, and blue may be used for the colorcomponents of the sub pixels. Furthermore, four or more colorscomprising red, green, blue, and at least one additional color may beused for the color components of the sub pixels.

Each of the sub pixels 42 has a switching element 45, a pixel electrode47, and a common electrode 48. The switching element 45 includes a thinfilm MOSFET. The circuit diagram illustrates that each of the pixels 40has a common electrode 48. Actually, however, the common electrodes 48are not provided separately. Those portions of each of the commonelectrodes 22 facing the respective pixel electrodes 47 (see FIG. 3 andFIG. 4) correspond to the common electrodes 48 of the respective subpixels 42. One common electrode 22 includes the common electrodes 48included in the sub pixels 42 constituting one or more pixels 40 (FIG. 2shows a case in which the sub pixels 42 constituting one pixel 40).

Sources of the switching elements 45 of the sub pixels 42 arranged alonga column of the pixel array 18 (Y axis) are connected to a common sourceline 44. The source lines 44 are connected through respective RGB selectswitches 104 to a source amplifier 118, as illustrated in FIG. 12 or thelike. Gates of the switching elements 45 arranged along a row of thepixel array 18 (X axis) are connected to a common gate line 46 (alsoreferred to as a scanning line). The gate lines 46 are connected to agate driver 102, as illustrated in FIG. 12 or the like. In the sub pixel42, a drain of the switching element 45 is connected to the pixelelectrode 47.

Since the common electrodes 48 of the sub pixels are included in thecommon electrode 22, a plurality of common electrode lines 50 (three inFIG. 2) are equivalent to the common electrode 22. The gate lines 46extend along X axis, and the source lines 44 extend along Y axis.Accordingly, the sub pixels 42 are formed near the respectiveintersections of the gate lines 46 and the source lines 44.

Cross Sectional Structure

FIG. 3 illustrates a cross sectional structure along X axis of thedisplay device of FIG. 1. A first optical device 52, a first substrate12, a liquid crystal layer 54, a second substrate 14, and a secondoptical device 56 are formed on the back light unit 36 in this order.Although FIG. 3 illustrates a structure of the display device using afringe field switching (FFS) mode as a display mode, other display modesmay be used. The first substrate 12 and the second substrate 14 arebonded together with a predetermined cell gap formed therebetween. Theliquid crystal layer 54 is held in the cell gap between the firstsubstrate 12 and the second substrate 14.

The first substrate 12 includes a first transparent insulating board 58,such as a glass substrate or a resin board. Although not illustrated,the source region, drain region and gate region of the switching element45 are formed in a surface area of the first insulating board 58 in aside of the second substrate 14. The first insulating layer 60 is formedon the surface of the first insulating board 58. A plurality of sourcelines 44 are formed on a surface of the first insulating layer 60. Eachof the source lines 44 extends along Y axis. Therefore, the source lines44 are arranged along X axis. A second insulating layer 62 is formed onthe surface of the first insulating layer 60.

A plurality of common electrodes 22 are formed on a surface of thesecond insulating layer 62. Each of the common electrodes 22 extendsalong Y axis. Therefore, the common electrodes 22 are arranged along Xaxis. The common electrode 22 is assigned to a plurality of source lines44, for example, three source lines 44 corresponding to three sub pixelsconstituting one pixel. The common electrodes 22 may be assigned to sucha number of the source lines 44 that is a multiple of three. Each of thecommon electrodes 22 is a stripe extending along Y axis. The commonelectrodes 22 are arranged along X axis. In order to make resistancelow, a metal layer 64 is formed on the surface of the common electrodes22. The metal layer 64 extends along Y axis. However, the metal layer 64may be omitted.

A third insulating layer 66 is formed on the surface of the secondinsulating layer 62. A plurality of pixel electrodes 47 are formed on asurface of the third insulating layer 66. Each of the pixel electrodes47 is located between the source lines 44. A portion of the commonelectrode 22 opposing the pixel electrode 47 corresponds to the commonelectrode 48 of the pixel 40 of FIG. 2. Each of the pixel electrodes 47may have a slit 68. Each of the pixel electrodes 47 is formed oftransparent materials, such as indium tin oxide (ITO) or indium zincoxide (IZO), so that a display may not be obstructed. The pixelelectrodes 47 and the third insulating layer 66 are covered with a firstalignment film 70.

The second substrate 14 includes a second transparent insulating board72, such as a glass substrate or a resin board. A black matrix 74 andcolor filters 76 _(R), 76 _(G), and 76 _(B) (generically named 76) areformed in a surface of the second insulating board 72 opposing the firstsubstrate 12. An overcoat layer 78 and a second alignment film 80 areformed at a surface of the second insulating board 72 facing the firstsubstrate 12.

The black matrix 74 is placed to divide each of the sub pixels. Thecolor filters 76 _(R), 76 _(G) and 76 _(B) partially overlap the blackmatrix 74. The color filters 76 _(R) transmits a light of a wavelengthcorresponding to red, the color filters 76 _(G) transmits a light of awavelength corresponding to green, and the color filters 76 _(B)transmits a light of a wavelength corresponding to blue. The overcoatlayer 78 covering the color filters 76 _(R), 76 _(G) and 76 _(B) isformed of a transparent resin material.

A plurality of detecting electrodes 24 are formed in an external surfaceof the second insulating board 72 (the upper side of FIG. 3). Each ofthe detecting electrodes 24 is a stripe extending along X axis. Thedetecting electrode 24 is placed along Y axis.

The back light unit 36 is placed at the back side (the lower side ofFIG. 3) of the display panel, as described above. The first opticaldevice 52 is placed between the first insulating board 58 and the backlight unit 36. The second optical device 56 is disposed above thedetecting electrode 24. The first optical device 52 and the secondoptical device 56 include at least a polarizer. The first optical device52 and the second optical device 56 may include a phase difference plateas needed.

Touch Detection Principle

FIG. 4 illustrates an exemplary basic structure of the touch panel 20according to a mutual sensing system. The detecting electrodes 24-1,24-2, . . . (generically named 24) formed in the second substrate 14 arestripes extending along X axis. The detecting electrodes 24 are arrangedalong Y axis. The common electrodes 22-1, 22-2, . . . (generically named22) formed in the first substrate 12 are stripes extending along Y axis.The common electrodes 22 are arranged along X axis. Accordingly, thedetecting electrodes 24 and the common electrodes 22 cross at rightangles on the touch panel 20. The source lines extend along Y axis, andare parallel to the common electrodes 22. This arrangement is called avertical COM type. The detecting electrodes 24 and the common electrodes22 perpendicularly crossing each other on the touch panel 20 may bearranged conversely to FIG. 4. That is, the detecting electrodes 24 arestripes extending along Y axis and the common electrodes 22 are stripesextending along X axis. In this case, the source lines and the commonelectrodes 22 cross each other. This arrangement is called a horizontalCOM type. In the following description, a vertical COM type isexplained. However, a horizontal COM type can be applied to theembodiment.

The liquid crystal layer 54 is between the first substrate 12 and thesecond substrate 14. The detecting electrodes 24 and the commonelectrodes 22 are separated with a gap therebetween. Therefore, thecapacitance C1 exists between the detecting electrodes 24 and the commonelectrodes 22. It is not necessary to provide one detecting electrode 24to each row in the pixel array. It is possible to provide one detectingelectrode 24 to two or more rows in the pixel array. It is not necessaryto provide one common electrode 22 to each column in the pixel array. Itis possible to provide one common electrode 22 to two or more columns inthe pixel array.

The common electrodes 22-1, 22-2, . . . are sequentially driven with adrive signal. A finger touches or is close to a crossing section atwhich the detecting electrode 24-3 and the common electrode 22-4 crosseach other. If a drive signal is supplied to the common electrode 22-4,detection signals are output from the detecting electrodes 24. Thedetection signal output from the detecting electrode 24-3 is lower inlevel than the detection signals output from other detecting electrodes24-1, 24-2, 24-4, 24-5, . . . . The detecting electrodes 24 monitor afringing field from the common electrodes 22. If a conductive objectsuch as a finger approaches, the fringing field is blocked, andcapacitance will change. The detection level of the detecting electrode24 is decreased. The mutual sensing touch sensor treats the differencein detection level as a detection signal indicative of a touch position.The drive signal supplied to one common electrode may be made of eithera single pulse or a plurality of pulses. The whole of the pulsessupplied to a plurality of common electrodes is called a drive signalTx. Accordingly, the drive signal Tx is a high frequency pulse signal.

The capacitance C1 is different in value between a case where a fingeris close to one of the detecting electrodes 24 and a case where a fingeris far from any of the detecting electrodes 24. Accordingly, thedetection signal will also be different in level depending on whetherthe finger is close to one of the detecting electrodes 24 or the fingeris far from any of the detecting electrodes 24. Accordingly, it possibleto determine the degree of proximity of the finger to the screen of adisplay panel based on the level of the detection signal. The positionof the screen touched by the finger may be detected based on the drivingtiming of the common electrodes 22 by means of the drive signal and theposition of a corresponding one of the detecting electrodes 24outputting a low level detection signal.

The common electrodes 22 are also used as driving electrodes driving aliquid crystal for display. Therefore, as illustrated in FIG. 5, aplurality of display periods are included in one frame period, touchdetection periods (also called non-display periods) are arranged betweenthe display periods. A display operation and a touch detection operationare performed in time sharing.

During a display period, the image signal Vsig from the host device 26for a plurality of lines is written in a display panel. The drive signalof a constant direct current voltage for display is supplied to all thecommon electrodes 22. An image of a plurality of lines is displayedaccording to the image signal. The image signal Vsig is formed of a setof pixel signals which are time division multiplex signals of the subpixel signals for a red, a green, and a blue sub pixel. The image signalVsig is divided into three colored sub pixel signals based on the RGBselect control signal SEL_(R/G/B). The number of lines displayed duringone display period is determined such that one frame is completelydisplayed within one frame period.

During a touch detection period, the drive signals Tx1, Tx2, Tx3, . . .are supplied to select one or more common electrodes 22. The selectedone or more common electrodes 22 change in voltage. The number of commonelectrodes 22 selected during a touch detection period is not limited toone. A plurality of common electrodes may be collectively driven duringa touch detection period. It may be arbitrarily established how manycommon electrodes are selected and driven during a touch detectionperiod.

In a mutual sensing touch sensor, common electrodes will not be drivensimultaneously. The common electrodes may be successively driven one byone or group by group. The former is called a simultaneous drive and thelatter a sequential drive. The sequential drive is not limited todriving a plurality of common electrodes in order, but includes drivinga plurality of common electrodes at random. Both a simultaneous driveand a sequential drive may be applicable to the self sensing touchsensor described later. Therefore, FIG. 5 may be applicable not only toa mutual sensing touch sensor but also a sequentially driven selfsensing touch sensor.

There are two drive methods for changing a voltage of a selected commonelectrode during a touch detection period based on a drive signal. Oneis a drive method (also called a DC drive), in which a pair of switchesconnected in series are connected to every common electrode. A highlevel voltage line and a low level voltage line are connected with eachother by the pair of switches. A middle point of the pair of switches isconnected to the common electrode. The pair of switches is turned on/offby the drive signal. The high level voltage or the low level voltage issupplied to the selected common electrode according to the level of thedrive signal. The other is a drive method (also called an AC drive)directly supplying a drive signal to the selected common electrode.

Now, the principle of self sensing touch detection will be explainedwith reference to FIG. 6A-FIG. 10. In a self sensing system, either thecommon electrode 22 or the detecting electrode 24 is used. For example,capacitance Cx1 of the common electrode 22 and capacitance Cx2 generatedby an electric conductor, such as a finger of the user, close to thecommon electrode 22 may be used.

FIGS. 6A and 6B illustrate a case where a user's finger neither touchesnor approaches a touch panel. The capacitance Cx2 is not generatedbetween the finger and the common electrode 22. FIG. 6A illustrates acase where a power source Vdd is connected to the common electrode 22through a control switch SWc. FIG. 6B illustrates a case where the powersource Vdd is disconnected from the common electrode 22 by the controlswitch SWc and a capacitance Ccp is connected to the common electrode 22through the control switch SWc.

The capacitance Cx1 is charged in the state illustrated in FIG. 6A. Thecapacitance Cx1 is discharged in the state illustrated in FIG. 6B.Charging of the capacitance Cx1 means that a constant signal is writteninto the common electrode 22 and that the common electrode 22 is drivenfor touch detection. Discharge of the capacitance Cx1 means that asignal indicative of change of the capacitance generated in the commonelectrode 22 is read. In order to execute the signal writing and thesignal reading, exclusive lines used for acquiring a detection signalmay be provided.

On the other hand, FIGS. 7A and 7B illustrate a case where a user'sfinger touches or is close to a touch panel. The capacitance Cx2 isgenerated between the finger and the common electrode 22. FIG. 7Aillustrates a case where the power source Vdd is connected to the commonelectrode 22 through the control switch SWc. FIG. 7B illustrates a casewhere the power source Vdd is disconnected from the common electrode 22by the control switch SWc and a capacitance Ccp is connected to thecommon electrode 22 through the control switch SWc.

The capacitance Cx1 is charged in the state illustrated in FIG. 7A. Thecapacitance Cx1 is discharged in the state illustrated in FIG. 7B.Voltage change characteristics of the capacitance Ccp at the time ofdischarge illustrated in FIG. 7B is clearly different from that of thecapacitance Ccp at the time of discharge illustrated in FIG. 6B becauseof existence of the capacitance Cx2. Therefore, in a self sensingsystem, input position information (for example, existence or absence ofan operational input) is determined using a change of the voltage changecharacteristics of the capacitance Ccp caused by the existence orabsence of the capacitance Cx2.

FIG. 8A illustrates an exemplary basic touch detection circuit accordingto the self sensing system. This circuit is provided in the touchsensing circuit 34 illustrated in, for example, FIG. 1. As illustratedin FIG. 8A, the common electrode 22 is connected to a first terminal ofa capacitance Cp for voltage division and a first input terminal of acomparator COMP. The common electrode 22 has its own capacitance Cx. Thecomparator COMP has a second input terminal connected to a power supplyof a reference voltage Vref.

A second terminal of the capacitance Cp is connected through the switchSW1 to a power source line Vcc. The second terminal of the capacitanceCp is connected through a resistor Rc to a first terminal of thecapacitance Cc. A second terminal of the capacitance Cc is connected toa reference potential (for example, a ground potential).

A switch SW2 is connected between the second terminal of the capacitanceCp and the reference potential. A switch SW3 is connected between thefirst terminal of the capacitance Cp and the reference potential.

Operation of the circuit illustrated in FIG. 8A will be explained. Theswitch SW1 is turned on in a fixed cycle, and charges the capacitanceCc. When the capacitance Cc is being charged, the switches SW2 and SW3are turned off. When the capacitance Cc is charged up, all the switchesSW1, SW2, and SW3 are turned off, and the charges of the capacitance Ccare kept.

Subsequently, the switches SW2 and SW3 are turned on for a fixed periodof time. The switch SW1 remains turned off. Then, almost all the chargesof both the capacitances Cp and Cx are discharged, and a part of thecharges of the capacitance Cc is discharged through the resistor Rc.

Subsequently, all the switches SW1, SW2, and SW3 are turned off. Then,the charges of the capacitance Cc move to the capacitances Cp and Cx.The equivalent circuit at this moment may be expressed as illustrated inFIG. 8B. Thereafter, the comparator COMP compares voltage Vx of thecapacitance Cx with the reference voltage Vref or a threshold voltageVth.

As apparent from the equivalent circuit illustrated in FIG. 8B, when allthe switches SW1, SW2, and SW3 are turned off, the charges of thecapacitance Cc move to the capacitances Cp and Cx, and then thecomparator COMP compares a variation in the voltage Vx of thecapacitance Cx with the reference voltage Vref. A series of theseoperations are repeated until the condition Vx<Vref is satisfied.

That is, after charging of the capacitance Cc is executed, the switchesSW2 and SW3 are kept in the on state for a fixed period of time. Theswitch SW1 remains turned off. Then, almost all the charges of thecapacitances Cp and Cx are discharged, and a part of the charges of thecapacitance Cc is discharged through the resistor Rc. Subsequently, allthe switches SW1, SW2, and SW3 are turned off. Then, the charges of thecapacitance Cc move to the capacitances Cp and Cx.

The relationships between the voltages Vp, Vc, and Vx, and thecapacitances Cp, Cc, Cx are expressed as follows.Vc=Vp+Vx  (1)Vp: Vx=(1/Cp):(1/Cx)  (2)Vx=(Cp/(Cp+Cx))×Vc  (3)

As described above, after the capacitance Cc is charged up to thevoltage Vc through the switch SW1, the switch SW1 is kept off state andthe switches SW2 and SW3 are repetitively turned on or off. Then, thevoltage Vc of the capacitance Cc will gradually be decreased, and thevoltage Vx of the capacitance Cx is decreased also. This operation,i.e., repeatedly turning on/off the switches SW2 and SW3 after thecapacitance Cc is charged up to the voltage Vc is continued until thevoltage Vx becomes lower than the reference voltage Vref.

FIG. 9 exemplarily illustrates a waveform of the voltage Vc of thecapacitance Cc, and a waveform of the output of the comparator COMP. Thehorizontal axis indicates time, and the vertical axis indicates thevoltage.

When the switch SW1 is turned on, the capacitance Cc is charged up tothe voltage Vcc. Thereafter, all the switches SW1, SW2, and SW3 areturned off, and the charges of the capacitance Cc move to thecapacitances Cp and Cx. Subsequently, the comparator COMP compares avariation in the voltage Vx of the capacitance Cx with the referencevoltage Vref.

A change characteristic or degree of change in the voltage Vc depends onthe sum total value of the capacitances Cp and Cx. The change of thecapacitance Cc will affect the voltage Vx of the capacitance Cx. Thecapacitance Cx will change in value according to how close a user'sfinger is to the common electrode 22.

Accordingly, as illustrated in FIG. 9, when the finger is far from thecommon electrode 22, a characteristic VCP1 with slow changes isobtained. When the finger is close to the common electrode 22, acharacteristic VCP2 with quick changes is obtained. The decreasing rateof the Vc is larger in the case where the finger is close to the commonelectrode 22 as compared with the case where the finger is far from thecommon electrode 22 because the finger has its own capacitance and thepresence of the finger will increase the capacitance Cc.

The comparator COMP compares the voltage Vp with the reference voltageVref or the threshold voltage Vth in synchronization with repetitiveturning on/off of the switches SW2 and SW3. When Vp is greater than Vref(Vp>Vref), the comparator COMP outputs a pulse. However, when Vp becomeslower than Vref (Vp<Vref), the comparator COMP stops outputting of thepulse.

The output pulse of the comparator COMP is monitored by a measuringapplication or a measuring circuit (not illustrated) inside the touchsensing circuit 34. That is, after the capacitance Cc has been chargedonce, repetitive discharging is carried out by the switches SW1 and SW2for a short period of time, and voltage Vp is repetitively measured.

At this moment, it is possible to measure the period (MP1 or MP2) of theoutput pulse from the comparator COMP or the number of the output pulsesof the comparator COMP. The number of the output pulses corresponds tothe number of pulses from the time when the capacitance Cc is fullycharged to the time when Vp becomes lower than Vref (Vp<Vref).

If a finger is far from the common electrode 22, the period MP1 or MP2is long. If a finger is close to the common electrode 22, the period isshort. If the finger is far from the common electrode 22, the number ofthe output pulses of the comparator COMP is large. If the finger isclose to the common electrode 22, the number of the output pulses of thecomparator COMP is small.

Accordingly, it is possible to determine the degree of proximity of thefinger to the touch sensor based on the level of the detection signal.If the common electrodes 22 are two-dimensionally arranged in a matrix,a two-dimensional position where the finger is placed on the touchsensor can be detected.

As described above, although it is detected whether or not the user'sfinger influences the common electrodes 22, the detection time is on theorder of several tens of μs to several ms.

FIG. 10 illustrates a common electrode drive method of a simultaneouslydriven self sensing system. In the same manner as FIG. 5, a plurality ofdisplay periods are included in one frame period, and touch detectionperiods (also called non-display periods) are arranged between thedisplay periods. In every touch detection period, the drive signals Tx1,Tx2, Tx3, . . . are supplied to the common electrodes 22-1, 22-2, 22-3,. . . .

The first embodiment may be similarly applicable to a mutual sensingtouch sensor.

Circuit Configuration

FIG. 11 is a circuit diagram exemplarily illustrating a construction ofthe display device. A gate driver 102 is provided outside one of the twolonger sides of the pixel array 18 on the first substrate 12 (forexample, a left-hand longer side). The RGB select switch (also called amultiplexer) 104 is provided outside one of the two shorter sides of thepixel array 18 on the first substrate 12 (for example, a bottom shorterside).

The display controller 16 includes a host I/F 112 connected to the hostdevice 26, and a touch panel I/F 122 connected to the touch sensingdevice 34. The image signal output from the host device 26 is receivedby the host I/F 112, and is supplied through an image memory 114, a linelatch circuit 116, the source amplifier 118, and the RGB select switch104 to the pixel array 18. The host I/F 112 subjects the image signaloutput from the host device 26 to an interpolation process, acompositing process, etc., and makes the image signal to be suitablydisplayed on the display device. The image memory 114 includes an SRAMor a DRAM or the like, and can store an image signal of one frame.

The line latch circuit 116 latches the image signal of one line outputfrom the image memory 114. An output of the line latch circuit 116 isconverted into an analog signal having gradation by the source amplifier118. The image signal output from the host device 26 is a time divisionmultiplex signal having three colored sub pixel signals of red, greenand blue. The image signal is separated into three colored respectivesub pixel signals by the RGB select switch 104 based on an RGB selectcontrol signal SEL_(R/G/B), and the separated three colored sub pixelsignals are supplied to the pixel array 18. As illustrated in FIG. 2,the switching elements 45 arranged in the row of the pixel array 18 areturned on by the gate driver 102 through the gate line 46. Sub pixelsignals are supplied through the turned-on switching elements 45 tocorresponding pixel electrodes 47. Since a constant direct currentvoltage is supplied to all the common electrodes 22 for display during adisplay period, an image is displayed by the sub pixels 42 according tothe pixel signals.

The control signal of the gate driver 102 and the RGB select controlsignal of the RGB select switch 104 are output from a panel controlsignal generator 124. The panel control signal generator 124 alsosupplies a control signal to the detecting electrodes 24 of the touchpanel 20. The detection signal of the touch panel 20 is supplied to thetouch sensing device 34. The common electrode of the pixel array 18 isdriven by the common electrode driver 126. The control signal of thecommon electrode driver 126 is output from the panel control signalgenerator 124. A DC driving method is used for driving the commonelectrode.

Although not illustrated, the common electrode driver 126 includes apair of switches connected in series and connected between a high levelvoltage line and a low level voltage line. An AC driving method may beused for driving the common electrode. The display controller 16includes a timing controller 128 determining operation timing of eachpart based on a synchronizing signal, a command, etc., output from thehost device 26, for example.

FIG. 12 illustrates a portion of the display controller 16 which drivesthe pixel matrix. The pixel signal output from the source amplifier 118is divided into three sub pixel signals of R, G, and B by the RGB selectswitches 104-1, 104-2, . . . (generically named 104). The sub pixelsignals indicative of three respective colors are supplied through therespective source lines 44-1, 44-2, and 44-3 (generically named 44) tothe respective sources of the switching elements 45 in the sub pixels 42_(R), 42 _(G) and 42 _(B). The sub pixels 42 _(R), 42 _(G) and 42 _(B)are constructed similarly to what is illustrated in FIG. 2. The subpixel signals are supplied to only those pixel electrodes 47 of the subpixels 42 through the switching elements 45 which are turned on by thegate driver 102. A predetermined number of source lines corresponding toone pixel 40, in FIG. 12, three source lines 44-1, 44-2, and 44-3, areconnected to the common electrode 22 through a SIG-COM switch 148. Thecommon electrode 22 is driven by the common electrode driver 126. TheRGB select switch 104 and the SIG-COM switches 148-1, 148-2, . . .(generically named 148) are turned on/off by the panel control signalgenerator 124.

The panel control signal generator 124 includes two voltage terminals162 and 164 and a guard terminal 166. The voltage terminal 162 is apositive voltage terminal, and the voltage terminal 164 is a negativevoltage terminal. The guard terminal 166 is connected through a couplingcapacitor 144 in the flexible printed circuit board 28 to the positivevoltage terminal 162, and is also connected through a coupling capacitor142 in the flexible printed circuit board 28 to the negative voltageterminal 164. The positive voltage terminal 162 and the negative voltageterminal 164 are also connected to the gate driver 102. The gate driver102 controls the potential of each of the gate lines 46 according to thevoltage of the positive voltage terminal 162 and the voltage of thenegative voltage terminal 164. It is possible to provide two gatedrivers 102 at both sides of the pixel array 18. In such a case, a halfof the gate drivers 102 is connected to the gate lines corresponding toodd-numbered pixel rows, and the other half of the gate drivers 102 isconnected to the gate lines corresponding to even-numbered pixel rows.The gate driver 102 includes a pair of switches 156 and 154 for drivingeach of the gate lines. The pair of switches 156 and 154 is connected inseries and is connected between the positive voltage terminal 162 andthe negative voltage terminal 164. The switches 156 and 154 are turnedon/off by the panel control signal generator 124.

The gate driver 102 supplies turn-on voltages to a plurality of gatelines 46 one after another during a display period, thereby selectinggate lines one after another. The turn-on voltage is applied to thegates of the switching elements 45 of the sub pixels 42 connected to theselected one of the gate lines 46. Thus, the switching elements 45 ofthe sub pixels 42 connected to the selected gate line 46 is conductive.

The source amplifier 118 supplies sub pixel signals through the RGBselect switches 104 to the source lines 44 during a display period. Thesub pixel signals supplied to the source lines 44 are supplied throughthe switching elements 45 that are conductive to the corresponding pixelelectrodes 47. The common electrode driver 126 supplies a constantdirect current voltage to the common electrodes 22 during a displayperiod.

The common electrode driver 126 supplies the drive signal Tx to one ormore common electrodes 22 during a touch detection period. The gatedriver 102 drives (also called guard-drives) all the gate lines 46during a touch detection period with a guard signal. The guard signal isa pulse signal that is the same in phase and amplitude as a pulse signalwhich constitutes the drive signal Tx. The amplitude does not mean anabsolute value of the amplitude level of the pulse but a differencebetween a high level and a low level.

Guard Drive of Gate Line

FIG. 13 illustrates a portion of the panel control signal generator 124which relates to a guard drive of a gate line. A positive external powersource VSP (for example, +5.5V) and a negative external power source VSN(for example, −5.5V) are respectively connected to a booster circuits170 and 180. The booster circuit 170 is a two-fold booster circuit, andoutputs a positive high voltage VGH of +11.0V, for example. The highvoltage VGH is decreased in voltage by an LDO regulator 172, and becomesa positive output voltage VGHO of +8.5V, for example.

The positive output voltage VGHO is supplied to a first terminal of aselector 174 connected to the positive voltage terminal 162. A secondterminal of the selector 174 is in a high impedance state. The selector174 selects the first terminal during a display period to set thepositive voltage terminal 162 at the positive output voltage VGHO, andselects the second terminal during a touch detection period to set thepositive voltage terminal 162 at a high impedance state. Although notillustrated, the high voltage VGH is also supplied to the pixel array 18and the touch panel 20, and is used for various power sources.

The booster circuit 180 is also a two-fold booster circuit, and outputsa negative high voltage VGL of −11.0V, for example. The negative highvoltage VGL is decreased in voltage by an LDO regulator 182, and becomesa negative output voltage VGLO of −8.5V, for example. The negativeoutput voltage VGLO is supplied to a first terminal of a selector 184connected to the negative voltage terminal 164. A second terminal of theselector 184 is in a high impedance state. The selector 184 selects thefirst terminal during a display period to set the negative voltageterminal 164 at the negative output voltage VGLO, and selects the secondterminal during a touch detection period to set the negative voltageterminal 164 at a high impedance state.

One or more common electrodes are selected during one touch detectionperiod. The drive signal Tx is supplied to the selected one or morecommon electrodes. In the common electrode driver 126, the pulse signalof a certain frequency is amplified to a predetermined voltage level,whereby and the drive signal Tx is generated. A difference (also calledamplitude) between the high level (for example, VSP=5.5V) and the lowlevel (for example, a ground level) is denoted by VHI. In the panelcontrol signal generator 124, a pulse signal which is a basis of thedrive signal is supplied to a terminal 175. The terminal 175 isconnected to a guard amplifier 176. The pulse signal input to theterminal 175 is amplified by the guard amplifier 176, whereby the guardsignal is generated. Therefore, the guard signal and the drive signal Txare the same in phase. An amplifier in the common electrode driver 126and the guard amplifier 176 in the panel control signal generator 124may be configured to amplify the signals such that the differencebetween the high level and the low level in the drive signal Tx issubstantially the same as the difference between the high level and thelow level in the guard signal.

The guard signal output from the guard amplifier 176 is supplied to afirst terminal of a selector 178 connected to the guard terminal 166. Asecond terminal of the selector 178 is grounded. The selector 178 iscontrolled by a guard enable signal. The selector 178 selects the firstterminal during an enable period to output the guard signal from theguard terminal 166, and selects the second terminal during a disableperiod to cause the guard terminal 166 to be grounded. The selectors174, 178, and 184 are switched over by the panel control signalgenerator 124. The selector may be constituted by a CMOS switchconnected between the first terminal and the second terminal andselecting either the first terminal or the second terminal according toa control signal.

The guard terminal 166 is connected to the positive voltage terminal 162through the coupling capacitor 144 in the flexible printed circuit board28, and is connected to the negative voltage terminal 164 through thecoupling capacitor 142 in the flexible printed circuit board 28. Thepositive voltage terminal 162 is connected through the switch 156 to thegate line 46, and the negative voltage terminal 164 is connected throughthe switch 154 to the gate line 46.

With reference to the timing chart of FIG. 14, the guard drive of thegate line by the panel control signal generator 124 of FIG. 13 isexplained. FIG. 14 illustrates the state of the selector 178 (waveform(a)), the state of the selectors 174 and 184 (waveform (c)). Theselector 178 is switched to the disabling side during a display period,and is switched to the enabling side during a touch detection period.The pulse signal which is the basis of the drive signal Tx is suppliedto the terminal 175 only during an enable period. When the selector 178switches from disabling to enabling, the guard signal in accordance withthe pulse signal input to the terminal 175 is output from the guardterminal 166, as illustrated by waveform (b) of FIG. 14. When theselector 178 switches from enabling to disabling, the guard terminal 166stops outputting the guard signal.

The positive voltage terminal 162 outputs the positive output voltageVGHO which is an output of the LDO regulator 172 during a displayperiod, as illustrated by waveform (d) of FIG. 14. The couplingcapacitor 144 is charged by the positive output voltage VGHO. Thecapacitance of the coupling capacitor 144 is determined such that thecurrent leakage from the coupling capacitor 144 can be disregarded andthe charges of the coupling capacitor 144 may be kept during a touchdetection period. Therefore, the positive voltage terminal 162 outputsduring a touch detection period a pulse signal in which the guard signaloutput from the guard terminal 166 is superposed on the positive outputvoltage VGHO having been charged in the coupling capacitor 144, asillustrated in waveform (d) of FIG. 14.

As illustrated in waveform (e) of FIG. 14, the negative voltage terminal164 outputs the negative output voltage VGLO which is an output of theLDO regulator 182 during a display period. The coupling capacitor 142 ischarged by the negative output voltage VGLO. The capacitance of thecoupling capacitor 142 is determined such that the current leakage fromthe coupling capacitor 142 can be disregarded and the charges of thecoupling capacitor 142 may be kept during a touch detection period.Therefore, the negative voltage terminal 164 outputs during a touchdetection period a pulse signal in which the guard signal output fromthe guard terminal 166 is superposed on the negative output voltage VGLOhaving been charged in the coupling capacitor 142, as illustrated inwaveform (e) of FIG. 14.

The gate line 46 is connected to the positive voltage terminal 162 ofthe panel control signal generator 124 through the switch 156 in thegate driver 102, and is also connected to the negative voltage terminal164 of the panel control signal generator 124 through the switch 154 inthe gate driver 102. The switch 156 is usually turned off and is turnedon only when the gate line 46 is turned on during a display period, asillustrated in waveform (f) of FIG. 14. The switch 154 is usually turnedon and is turned off only when the gate line 46 is turned on during adisplay period, as illustrated in waveform (g) of FIG. 14. Accordingly,as illustrated in waveform (h) of FIG. 14, the negative output voltageVGLO is usually supplied to the gate line 46 during a display period.Only when the switch 154 is turned off and the switch 156 is turned onduring a display period, the positive output voltage VGHO is supplied tothe gate line 46, whereby the switching element 45 is turned on.

During a touch detection period, the gate line 46 is supplied with apulse signal in which the guard signal output from the guard terminal166 is superposed on the negative output voltage VGLO generated at thenegative voltage terminal 164. The signal generated at the terminal 164is a negative voltage. Therefore, even if a signal in which the guardsignal is superposed on the signal of the terminal 164 is supplied tothe gate line 46, the switching elements 45 of sub pixels are not turnedon.

The guard signal is a pulse signal which is the same in phase andamplitude as the drive signal Tx supplied to the common electrode duringa touch detection period. Accordingly, the gate line 46 is driven by apulse in the same amplitude and phase as the drive signal Tx during atouch detection period. Therefore, parasitic capacitance is less likelyconnected between the common electrode and the gate line. The load ofthe common electrode is reduced.

The RGB select switch 104 sequentially selects the R, G and B sub pixelsduring a display period and is turned off during a touch detectionperiod, as illustrated in waveform (i) of FIG. 14. Therefore, the sourceline 44 is in a high impedance state during a touch detection period.The SIG-COM switch 148 is turned off during a display period and isturned on during a touch detection period, as illustrated in waveform(j) of FIG. 14. All the SIG-COM switches 148 may be turned on during atouch detection period, whereas, in the case of a sequential drive, onlythose SIG-COM switches 148 that are connected to the common electrodes22 to each the drive signal Tx is supplied may be turned on. Therefore,the common electrode 22 and the source line 44 are short-circuitedduring a touch detection period. The drive signal Tx (waveform (k) ofFIG. 14) supplied to the common electrode 22 is also supplied throughthe SIG-COM switch 148 to the source line 44. Thereby, the influence ofthe parasitic capacitance between the common electrode 22 and the sourceline 44 is reduced, and it becomes possible to drive the commonelectrode 22 at a desired waveform with the drive signal Tx.

The common electrode 22 is made of, for example, transparent electrodematerials, such as ITO or IZO. The source line 44 is usually made ofmetal. Therefore, the common electrode 22 is higher in resistance thanthe source line 44. When the common electrode 22 and the source line 44are short-circuited during a touch detection period, the commonelectrode 22 will decrease in resistance, and electric power consumptionwill decrease.

As illustrated in waveform (k) of FIG. 14, the common electrode driver126 for driving the common electrode 22 outputs constant direct currentvoltage during a display period, and outputs the drive signal Tx, whichis a high frequency pulse, during a touch detection period.

As described above, during a touch detection period, the drive signal Txis supplied to the common electrodes 22-1, 22-2, . . . and the guardsignal is supplied to the gate lines 46, which intersect the commonelectrodes 22. The guard signal is a pulse signal that is the same inamplitude and phase as the drive signal. Therefore, parasiticcapacitance is less likely connected between the common electrode 22 andthe gate line 46 in the pixel array 18. Therefore, the common electrode22 driven by the drive signal in a touch detection period improves inresponse characteristics. Detection accuracy is improved and detectiontime is shortened. Furthermore, since the source line 44 and the commonelectrode 22 are short circuited during a touch detection period,parasitic capacitance is less likely connected between the source line44 and the common electrode 22 in the pixel array 18, or between thesource line 44 and the gate line 46 in the pixel array 18. Therefore,the influence of the parasitic capacitance in the pixel array 18 causedby the drive signal of the common electrode can be suppressed during atouch detection period.

Select Switch

FIG. 15 illustrates a portion relating to generation of a select controlsignal of the RGB select switch 104 in the panel control signalgenerator 124. CMOS switches 190 _(R), 190 _(G), and 190 _(B) areconnected as selectors between the external power sources VSP and VSN.The CMOS switch 190 includes a PMOSFET and an NMOSFET connected inseries. In the CMOS switch 190, the PMOSFET is connected to the powersource VSP, the NMOSFET is connected to the power source VSN, and thegate of the PMOSFET and the gate of the NMOSFET are commonly connectedto a clock terminal CLK. The CMOS switch 190 outputs either VSP or VSNfrom the connection point of both FETs according to the level of theclock terminal CLK. The output of the COMS switch 190 is suppliedthrough an inverter 191 to the select switch 104 as the select controlsignals sel_(R), sel_(G), or sel_(B). The power source of the inverter191 is connected to the power sources VSP and VSN so that the voltagedriving the next stage can be output.

The select switch 104 includes switches 104 _(R), 104 _(G), and 104 _(B)which respectively transmit or shut red, green, and blue sub pixelsignals. Each of the switches 104 _(R), 104 _(G), and 104 _(B) includesa CMOS transfer gate including a PMOSFET 192 and an NMOSFET 196. Theselect control signal sel_(R), sel_(G), or sel_(B) is supplied to a gateof the NMOSFET 196, and is supplied through an inverter 194 to a gate ofthe PMOSFET 192, as an inverted select control signal sel_(XR),sel_(XG), or sel_(XB). The inverter 194 has a power source connected tothe power sources VSP and VSN so that the voltage driving the next stagecan be output.

FIG. 16 is a timing chart indicative of the select control signalssel_(R), sel_(G), and sel_(B) generated by the panel control signalgenerator 124 of FIG. 15. As illustrated at waveforms (a), (d), and (g)in FIG. 16, clocks CLK_(R), CLK_(G), and CLK_(B) are pulse signalshaving the same cycle and shifted by one pulse period. The clocksCLK_(R), CLK_(G), and CLK_(B) are generated during a display period, andare not generated during a touch detection period. The CMOS switches 190_(R), 190 _(G), and 190 _(B) respectively output negative voltages VSNwhen the clocks CLK_(R), CLK_(G), and CLK_(B) are in a high level, andoutput positive voltages VSP when the clocks CLK_(R), CLK_(G), andCLK_(B) are in a low level. The outputs of the CMOS switches 190 _(R),190 _(G), and 190 _(B) are inverted by the respective inverters 191, sothat the select control signals sel_(R), sel_(G), and sel_(B) aresignals which synchronize with the respective clocks CLK, as illustratedat waveforms (b), (e), and (h) in FIG. 16. The inverted select controlsignals sel_(XR), sel_(XG), and sel_(XB) are illustrated at waveforms(c), (f), and (i) in FIG. 16. Thereby, the select switches 104 areturned on when the select control signals sel_(R), sel_(G), and sel_(B)are in high levels.

Now, other embodiments will be explained. Each of the other embodimentsis a partial modification of the first embodiment. It is possible tocombine any numbers of the other embodiments together.

Second Embodiment

In the first embodiment, as illustrated in waveform (h) of FIG. 14, thegate line 46 in the pixel array 18 and the source line 44 are driven bythe guard signal in synchronization with the drive signal Tx for touchdetection during a touch detection period. The drive signal is suppliedto the source line 44 when the SIG-COM switch 148 is turned on. In thefirst embodiment, as illustrated in waveform (i) of FIG. 14, the RGBselect switches 104 are sequentially turned on to divide a pixel signalinto sub pixel signals during a display period, and are turned offduring a touch detection period. Therefore, parasitic capacitance mayoccur in the control signal lines of the RGB select switches 104 duringa touch detection period. A second embodiment suppressing an influenceof the parasitic capacitance in the control signal lines will beexplained. Similarly to the first embodiment, the second embodiment maybe also applicable to both a self sensing touch sensor and a mutualsensing touch sensor.

FIG. 17 is a circuit diagram illustrating a select control signal (SEL)generator 202 _(R) for the RGB select switch 104 in the panel controlsignal generator 124 according to the second embodiment. Other colorselect control signal generators 202 _(G) and 202 _(B) are similarlyconstructed. A touch detection period signal (high level during a touchdetection period) and a guard enable signal are input to an AND gate204.

PMOSFETs 205 and 206 are connected in series between the positivevoltage terminal 162 and the external power source VSP. The PMOSFET 205is connected to the positive voltage terminal 162, and the PMOSFET 206is connected to the external power source VSP. An output of the AND gate204 is connected to a gate of the PMOSFET 206. The output terminal ofthe AND gate 204 is also connected through an inverter 207 to a gate ofthe PMOSFET 205. The inverter 207 has a power source, which is connectedto the ground and the positive voltage terminal 162, so that a voltagedriving a next stage can be output.

An NMOSFET 208 and a PMOSFET 209 are connected in series between thenegative voltage terminal 164 and the external power source VSN. TheNMOSFET 208 is connected to the negative voltage terminal 164, and thePMOSFET 209 is connected to the external power source VSN. The outputterminal of the AND gate 204 is connected to gates of the NMOSFET 208and the PMOSFET 209.

A PMOSFET 210 and an NMOSFET 212 are connected in series between aconnection point of the PMOSFETs 205 and 206, and a connection point ofthe NMOSFET 208 and the PMOSFET 209. The PMOSFET 210 is connected to theconnection point of the PMOSFETs 205 and 206. The NMOSFET 212 isconnected to the connection point of the NMOSFET 208 and the PMOSFET209.

Clock CLK_(R) is connected through a level shifter 214 and an inverter215 to gates of the PMOSFET 210 and the NMOSFET 212. A connection pointof the PMOSFET 210 and the NMOSFET 212 is connected to a first terminal216 a of the selector 216. A second terminal 216 b of the selector 216is connected to the positive voltage terminal 162. The selector 216 iscontrolled by the guard enable signal, and selects the first terminal216 a during a disable period and the second terminal 216 b during anenable period. The select control signal SEL_(R) is output from theselector 216 to the gate of the NMOSFET 196 in the switch 104 _(R). Theinverter 215 has a power source connected to both the connection pointof the PMOSFETs 205 and 206 and the connection point of the NMOSFET 208and the PMOSFET 209 so that a voltage driving the next stage can beoutput.

The connection point of the PMOSFET 210 and the NMOSFET 212 is connectedthrough an inverter 224 to a first terminal 217 a of a selector 217. Theselector 217 has a second terminal 217 b connected to the negativevoltage terminal 164. The selector 217 is also controlled by the guardenable signal, and selects the first terminal 217 a during a disableperiod and the second terminal 217 b during an enable period. Theinverted select control signal SELXR is output from the selector 217 tothe gate of the PMOSFET 192 in the switch 104 _(R). The inverter 224 hasa power source connected to the ground and the external input power VSPso that a voltage driving the next stage can be output. It should benoted that level shifters may be connected to the gates of the PMOSFETs205, 206, the NMOSFET 208, and the PMOSFET 209.

FIG. 18 is a timing chart illustrating the select control signalsSEL_(R) and SEL_(XR) generated by the select control signal generator202 _(R) of FIG. 17. Waveforms (a) and (b) in FIG. 18 respectivelyillustrate the guard enable signal and the touch detection periodsignal. The guard enable signal is in a high level during an enableperiod, and the touch detection period signal is in a high level duringa touch detection period. Similarly to the timing chart of FIG. 14, theguard enable signal is disabled (in a low level) during a displayperiod, and is enabled (in a high level) during a touch detectionperiod. The touch detection period signal is in a low level during adisplay period and is in a high level during a touch detection period.Therefore, as illustrated in waveform (c) of FIG. 18, an output of theAND gate 204 is in a low level during a display period, and is in a highlevel during a touch detection period. The clock CLK_(R) illustrated inwaveform (d) of FIG. 18 is the same clock as the waveform (a) in FIG.16. The clock CLK_(R) is generated during a display period, but is notgenerated during a touch detection period.

During a display period, the output of the AND gate 204 is in a lowlevel and the PMOSFETs 206 and 209 are turned on. The selectors 216 and217 respectively select the first terminals 216 a and 217 a. The PMOSFET210 and the NMOSFET 212 are turned on according to whether the clockCLK_(R) is in a high level or in a low level. Therefore, the selectcontrol signal SEL_(R) is in a VSP level or in a VSN level during adisplay period according to whether the clock CLK_(R) is in a high levelor in a low level, as illustrated in waveform (g) of FIG. 18. Theinverted select control signal SEL_(XR) is in a low level or in a highlevel during a display period according to whether the clock CLK_(R) isin a high level or in a low level, as illustrated in waveform (h) ofFIG. 18.

During a touch detection period, the output of the AND gate 204 is in ahigh level and the PMOSFET 205 and the NMOSFET 208 are turned on. Theselectors 216 and 217 select the second terminals 216 b and 217 b.Therefore, as illustrated in waveform (g) of FIG. 18, the select controlsignal SEL_(R) becomes a signal which is the same as a signal outputfrom the terminal 162 during a touch detection period. The invertedselect control signal SEL_(XR) becomes a signal which is the same as asignal output from the terminal 164 during a touch detection period, asillustrated in waveform (h) of FIG. 18. Accordingly, the select controlsignal SEL_(R) is a pulse signal in which the guard signal is superposedon the positive output voltage VGHO, and the inverted select controlsignal SEL_(XR) is a pulse signal in which the guard signal issuperposed on the negative output voltage VGLO.

As described above, in the second embodiment, the select control signalof the RGB select switch 104 is subjected to amplitude modulation duringa touch detection period according to the guard signal whichsynchronizes with the drive signal Tx. Accordingly, parasiticcapacitance between the select signal line and the source line orbetween the inverted select signal line and the source line is hardlygenerated in the wiring area outside the pixel array 18.

Furthermore, in the second embodiment, the select control signalfluctuates in level between VSP (for example, +5.5V) and VSN (forexample, −5.5V) during a display period. However, the low level of theselect control signal is kept at VGHO, which is higher than VSP, duringa touch detection period. On the other hand, similarly to the firstembodiment, the SIG-COM switch 148 is turned on during a touch detectionperiod, the drive signal Tx from the common electrode driver 126 returnsfrom the common electrode 22 through the source line 44 to the RGBselect switch 104. If the select control signal fluctuates in levelbetween VSP and VSN during a touch detection period similarly to thedisplay period, noises etc., may mix in the select control signal. Ifnoises etc., will mix in the select control signal, the RGB selectswitch 104 will turn on. Then, a drive signal is input through the RGBselect switch 104 into the source amplifier 118. Therefore, there is apossibility that the source amplifier 118 may be destroyed. However, theselect control signal and the inverted select control signal illustratedin waveforms (g) and (h) of FIG. 18 are generated in the secondembodiment. These signals cause the RGB select switch 104 to be turnedoff during a touch detection period.

The second embodiment may be applicable to a mutual sensing touchsensor. In such a case, drive signals should be supplied to the commonelectrodes one after another as illustrated in FIG. 5. Accordingly, whatis subjected to a guard drive is only a select control signal suppliedto an RGB select switch 104 corresponding to a source line whichcorresponds to a selected one of the common electrodes to which thedrive signal is supplied. In order to achieve it, a SEL signal generatormay be provided to each of the select switches 104 that are connected tothe respective source lines.

Third Embodiment

A third embodiment will be explained relating to a modification of theselect control signal generator of the second embodiment. FIG. 19 is acircuit diagram of the select control (SEL) signal generator 222 _(R) ofthe third embodiment. The select control signal generators 222G and 222Bfor the other colors are similarly constructed. In the first embodimentor the second embodiment, it is possible to provide the select controlsignal generator in the display control circuit 16 or on the firstsubstrate 12 similarly to the gate driver 102 or the RGB select switches104. However, in the third embodiment, the generator 222 is provided onthe first substrate 12. Similarly to the first and the secondembodiment, the third embodiment may also be applicable to both a selfsensing touch sensor and a mutual sensing touch sensor.

PMOSFETs 221 and 220 are connected in series between the positivevoltage terminal 162 and a terminal to which the select control signalsel_(R) of FIG. 15 is supplied. The PMOSFET 221 is connected to theselect control signal sel_(R) terminal, and the PMOSFET 220 is connectedto the positive voltage terminal 162.

An NMOSFET 223 and a PMOSFET 222 are connected in series between thenegative voltage terminal 164 and a terminal to which the invertedselect control signal sel_(XR) of FIG. 15 is supplied.

The touch detection period signal and the guard enable signal are inputto an AND gate 218. An output of the AND gate 218 is connected to a gateof the PMOSFET 221. The output of the AND gate 218 is also connectedthrough an inverter 232 to gates of the PMOSFETs 220 and 222 and theNMOSFET 223.

The select control signal SEL_(R) is output from a connection point ofthe PMOSFETs 221 and 220 to a gate of an NMOSFET 196 in the switch 104_(R). An inverted select control signal SEL_(XR) is output from aconnection point of the NMOSFET 223 and the PMOSFET 222 to a gate of thePMOSFET 192 in the switch 104 _(R).

FIG. 20 is a timing chart illustrating the select control signalsSEL_(R) and SEL_(XR) generated by the select control signal generator222 _(R) of FIG. 19. Similarly to waveforms (a) and (b) in FIG. 18,waveforms (a) and (b) in FIG. 20 respectively indicate the guard enablesignal and the touch detection period signal. An output of the AND gate218 is high in level during a touch detection period, as illustrated inwaveform (c) of FIG. 20.

The output of the AND gate 218 is low in level during a display period,so that the PMOSFET 221 and the NMOSFET 223 are turned on. As a result,as illustrated in waveform (h) of FIG. 20, the select control signalSEL_(R) is the same as the select control signal sel_(R) (waveform (f)of FIG. 20) during a display period. As illustrated in waveform (i) ofFIG. 20, the inverted select control signal SEL_(XR) is the same as theinverted select control signal sel_(R) (waveform (g) of FIG. 20) duringa display period.

The output of the AND gate 218 is high in level during a touch detectionperiod, so that the PMOSFETs 220 and 222 are turned on. As a result, asillustrated in waveform (h) of FIG. 20, the select control signalSEL_(R) is the same as the signal of the terminal 162 (waveform (d) ofFIG. 20) during a touch detection period. As illustrated in waveform (i)of FIG. 20, the inverted select control signal SEL_(XR) is the same asthe signal of the terminal 164 (waveform (e) of FIG. 20).

Therefore, the generator 222 of FIG. 19 can generate similarly to FIG.18 the select control signal SEL_(R), which is a pulse signal obtainedby superposing the guard signal on the positive output voltage VGHO, andthe inverted select control signal SEL_(XR), which is a pulse signalobtained by superposing the guard signal on the negative output voltageVGLO. Therefore, the generator 222 of FIG. 19 can obtain the same effectas the second embodiment.

The third embodiment may be applicable to a mutual sensing touch sensor.In such a case, drive signals should be supplied to the commonelectrodes one after another as illustrated in FIG. 5. Accordingly, whatis subjected to a guard drive is only a select control signal suppliedto an RGB select switch 104 corresponding to a source line whichcorresponds to a selected one of the common electrodes to which thedrive signal is supplied. In order to achieve it, a SEL signal generatormay be provided to each of the select switches 104 that are connected tothe respective source lines.

Fourth Embodiment

In the second and the third embodiment, what is subjected to a guarddrive during a touch detection period is the select control signal ofthe RGB select switch 104. A fourth embodiment applied to a self sensingtouch sensor is explained in which the input signals to the RGB selectswitches 104, i.e., the output signals of the source amplifier 118 aresubjected to a guard drive during a touch detection period, and all thedriving electrodes are simultaneously driven.

Since a liquid crystal will deteriorate if direct current voltage iscontinuously supplied, the voltage supplied to the source lines maysometimes be AC driven. The AC drive includes a dot reverse system, inwhich every frame is subjected to such a reverse driving that verticallyand horizontally adjacent pixels are reversed in polarity, and a columnreverse system, in which every frame is subjected to such a reversedriving that horizontally adjacent pixels are reversed in polaritywithout reversing vertically adjacent pixels. The fourth embodiment willbe explained with taking a column reverse system as an example.

The source amplifier includes, as illustrated in FIG. 21D, a positivepolarity amplifier 248 operated by a positive power source and anegative polarity amplifier 249 operated by a negative power source. Forexample, in a certain frame, an image signal for an odd-numbered sourceline is supplied to the positive polarity amplifier 248, and an imagesignal for an even numbered source line is supplied to the negativepolarity amplifier 249. During a touch detection period, an output ofthe positive polarity amplifier 248 is subjected to a guard drive and anoutput of the negative polarity amplifier 249 is set to a high impedancestate. An example for subjecting the output signal of the positivepolarity amplifier 248 to a guard drive is illustrated in FIGS. 21A,21B, and 21C.

The positive polarity amplifier 248 in FIG. 21A includes a positivepolarity operational amplifier 248A having an input terminal connectedto the terminal 175 (FIG. 13). The pulse signal, the basis of the drivesignal Tx, is supplied to the positive polarity operational amplifier248A during a touch detection period. The operational amplifier 248A isoperated by the external power sources VSP and VSN. An image signal isinput to the operational amplifier 248A during a display period. Duringa touch detection period, the operational amplifier 248A amplifies thepulse signal of the terminal 175 and outputs the guard signal (refer towaveform (b) of FIG. 14) which is a pulse having an amplitude of VHI.

In FIG. 21A, the operational amplifier 248A itself amplifies the pulse,which is the basis of the drive signal Tx, and generates the guardsignal. However, it is possible to use an ordinary amplifier as theoperational amplifier 248A. In such a case, the guard signal may beapplied to the output terminal of the amplifier only during a touchdetection period, thereby outputting the guard signal from the outputterminal of the operational amplifier 248A. Some examples areillustrated in FIGS. 21B and 21C.

In the amplifier 248 of FIG. 21B, ON/OFF switches 248C, 248D, and 248Eare connected to an output terminal of the operational amplifier 248A towhich an image signal is supplied. The ON/OFF switches 248D and 248E areconnected in series between the external power source VSP and theground. The ON/OFF switch 248C is connected between the output terminalof the operational amplifier 248A and a connection point of the ON/OFFswitches 248D and 248E. During a touch detection period, the switch 248Cis turned off, and the switches 248D and 248E are alternately turned onand off in synchronism with the drive signal Tx. Thereby the outputlevel of the operational amplifier 248A fluctuates between a groundlevel and the external power source VPN. Therefore, the guard signal asillustrated in waveform (b) of FIG. 14 is output from the operationalamplifier 248A.

The amplifier 248 of FIG. 21C include an ON/OFF switch 248F connected tothe output terminal of the operational amplifier 248A and a positivepolarity operational amplifier 248G. An input of the operationalamplifier 248G is connected to the terminal 175. The pulse signal whichis similar to the guard signal is output by turning off the switch 248Fduring a touch detection period. This structure also makes it possibleto cause the output terminal of the operational amplifier 248A to outputthe guard signal as illustrated in waveform (b) of FIG. 14.

For example, an output of the positive polarity amplifier 248constituted as illustrated in FIGS. 21A, 21B, and 21C is connected tofirst terminals of selectors 238 and 242 through a selector 236. A firstterminal of the selector 236 is connected to the first terminal of theselector 238. A second terminal of the selector 236 is connected to thefirst terminal of the selector 242. An output of a negative polarityamplifier 249 is connected to second terminals of the selectors 238 and242 through a selector 240. A first terminal of the selector 236 isconnected to the second terminal of the selector 238. A second terminalof the selector 240 is connected to the second terminal of the selector242.

An output of the selector 238 is supplied to an odd-numbered source lineS1, and an output of the selector 242 is supplied to an even-numberedsource line S2. The source lines S1 and S2 are respectively connected tothe RGB select switches 104-1 and 104-2. Outputs of the positivepolarity amplifier the negative polarity amplifier are similarlysupplied to other source lines.

The selectors 236, 238, 240, and 242 are switched for every frame. Theselectors 236, 238, 240, and 242 are selected such that the output ofthe positive polarity amplifier 248 is supplied to the source line S1and the output of the negative polarity amplifier 249 is supplied to thesource line S2 at a certain frame, for example, at every odd frame, andthe output of the positive polarity amplifier 248 is supplied to thesource line S2 and the output of the negative polarity amplifier 249 issupplied to the source line S1 at every even frame.

Waveforms (a) and (b) of FIG. 22 respectively illustrate the selectioncontrol signal SEL_(R/G/B) and the inverted selection control signalSEL_(XR/XG/XB), both for the RGB select switch 104 of a certain frame,for example, an odd frame. Waveforms (c) and (d) of FIG. 22 respectivelyillustrate a signal level exhibited by the source line S1 and a signallevel exhibited by the source line S2.

In this way, the guard signal is output during a touch detection periodfrom the source amplifier 118 (the positive polarity amplifier 248).Therefore, the parasitic capacitance is hardly generated between thecommon electrode 22 and a corresponding one of the output lines of thesource amplifier 118 (signal lines between the source amplifier 118 andthe RGB select switches 104).

Fifth Embodiment

In a fifth embodiment, the guard signal is output from the sourceamplifier 118 during a touch detection period similarly to the fourthembodiment. The fourth embodiment is applied to a simultaneously drivenself sensing system, whereas the fifth embodiment is applied to a mutualsensing touch sensor. As described above, a mutual sensing touch sensorsequentially selects the common electrodes 22-1, 22-2, . . . during atouch detection period, and sequentially supplies the driving signalsTx1, Tx2, . . . to the selected common electrodes.

In the fourth embodiment concerning a simultaneously driven self sensingtouch sensor, the positive polarity amplifier 248 of the sourceamplifier 118 outputs the guard signal sufficient for all the pixels inone line during a touch detection period. In the mutual sensing touchsensor of the fifth embodiment, as illustrated in FIG. 23, commonelectrodes are selected one by one. The guard signals are output fromonly those positive polarity amplifiers in the source amplifier 118 thatcorrespond to a selected one of the common electrodes. The guard signalsare not output from the remaining positive polarity amplifiers in thesource amplifier 118 that do not correspond to the selected one of thecommon electrodes. First positive polarity amplifiers that output theguard signal during a touch detection period are named positive polarityamplifiers (+) 254, and second positive polarity amplifiers that do notoutput any guard signal during a touch detection period are namedpositive polarity amplifiers (+′) 256.

The output of each of the positive polarity amplifiers (+′) 256 is in ahigh impedance state during a touch detection period. The positivepolarity amplifier 248 illustrated in FIGS. 21A, 21B, and 21C may beused for the first positive polarity amplifiers (+) 254 and the secondpositive polarity amplifiers (+′) 256. The positive polarity amplifier248 may be used as either the first positive polarity amplifier or thesecond positive polarity amplifier by controlling outputting of theguard signal from the positive polarity amplifier 248 during a touchdetection period. A negative polarity amplifier (−) 258 is the same asthe negative polarity amplifier 249 illustrated in FIG. 21D, outputs anegative polarity pixel signal during a display period, and outputs ahigh impedance signal during a touch detection period.

The common electrode driver 126 outputs a constant voltage VCOMDC fordisplay during a display period, and outputs drive signals Tx1, Tx2, . .. to the respective common electrodes 22-1, 22-2, . . . during a touchdetection period.

A voltage select switch 252 for connecting either the voltage VCOMDC orthe drive signal Tx to the source line during a touch detection periodis connected between the RGB select switch 104 and the common electrode22. The panel control signal generator 124 switches the voltage selectswitch 252 such that a source line corresponding to the selected commonelectrode is connected to the drive signal Tx1, and that source linescorresponding to non-selected common electrodes are connected to thevoltage VCOMDC.

Accordingly, the guard signal from the source amplifier 118 (thepositive polarity amplifier 254) is added to the drive signal Tx outputfrom the common electrode driver 126 to the common electrode 22 during atouch detection period. Therefore, in comparison with a case where thecommon electrode 22 is driven only by the drive signal Tx, the drivesignal Tx in a display panel is improved in slew rate, and touchdetection is improved in accuracy.

The fifth embodiment may be applicable to a self sensing touch sensor solong as the touch sensor is sequentially driven.

Sixth Embodiment

According to the fifth embodiment, the guard signal output from thesource amplifier 118 is added to the drive signal Tx output from thecommon electrode driver 126 to the common electrode 22 during a touchdetection period. The fifth embodiment may also be applicable to amutual sensing touch sensor having an ordinary two-chip structure(comprising a display controller IC and a touch controller IC).

In the ordinary display device having a two-chip structure, the commonelectrode driver 126B does not output the drive signals Tx1, Tx2, . . .to the respective common electrodes 22-1, 22-2, but outputs a singledrive signal TSVCOM to all the common electrodes. The drive signalTSVCOM is supplied as the drive signal Tx only to a selected commonelectrode selected by the TSVCOM select switch 264. The TSVCOM selectswitch 264 includes switches assigned to the respective commonelectrodes 22-1, 22-2, . . . . The common electrode driver 126B alsooutputs a constant voltage VCOMDC. The constant voltage VCOMDC issupplied to non-selected common electrodes through a VCOMDC selectswitch 262. The VCOMDC select switch 262 includes switches assigned tothe respective common electrodes 22-1, 22-2, . . . .

In such an ordinary two-chip structured touch sensor, a drive signalsupply source is only a TSVCOM terminal. If a load of the drive signalTx is large, a settling characteristic may be deteriorated.

However, as illustrated in FIG. 24, an output of the source amplifier118 is supplied through the RGB select switch 104 to the pixel 40 andalso supplied through the SIG-COM switch 148 to selected commonelectrode 22. The SIG-COM switch 148 short-circuits the common electrode22 and the source line 44 during a touch detection period.

A constant direct current voltage VCOMDC output from the commonelectrode driver 126B is supplied through the VCOM select switch 262 tonon-selected common electrodes 22. T drive signal TSVCOM output from thecommon electrode driver 126B is supplied through the TSVCOM selectswitch 264 to the selected common electrode 22. The VCOM select switch262 and the TSVCOM select switch 264 are connected in series between thevoltage VCOMDC line and the voltage TSVCOM line. A connection point ofthe VCOM select switch 262 and the TSVCOM select switch 264 is connectedto the common electrode 22. During a display period, the switch 262 isturned on and the switch 264 is turned off. Therefore, the directcurrent voltage VCOMDC is supplied to the common electrode 22 during adisplay period. States of the switches 262 and 264 corresponding to anon-selected common electrode 22-2, for example, during a touchdetection period are the same as states of the switches 262 and 264during a display period. The switches 262 and 264 corresponding to aselected common electrode, for example, 22-1, are turned off and onduring a touch detection period. Therefore, the drive signal TSVCOM issupplied to the common electrodes 22 during a touch detection period.

The source amplifier 118 is constructed as FIG. 23. Accordingly, thesource amplifier 118 corresponding to the selected common electrode 22-1includes the first positive polarity amplifiers (+) 254 and the negativepolarity amplifiers (−) 258. The source amplifier 118 corresponding tothe non-selected common electrode 22-2 includes the second positivepolarity amplifiers (+′) 256 and the negative polarity amplifiers (−)258.

The common electrode driver 126B and the source amplifier 118 areprovided in the display controller (display controller IC) 16, and theRGB select switch 104, the VCOM select switch 262, the TSVCOM selectswitch 264, and the SIG-COM switch 148 are provided in a display panel.

FIG. 25 is a timing chart indicative of a driving of the selected commonelectrode. Waveform (a) of FIG. 25 illustrates the drive signal Txsupplied to the selected driving electrode. Waveform (b) of FIG. 25illustrates an operation of the source amplifier 118. Waveform (c) ofFIG. 25 illustrates the select control signal SEL_(R/G/B) supplied tothe select switch 104. During a display period, the drive signal Tx isin a low level, the select control signal SEL_(R/G/B) sequentiallyselects RGB, and the source amplifier 118 outputs an image signal.During a touch detection period, the drive signal Tx is a pulse signalof a high level and a low level, and the select control signalSEL_(R/G/B) is a pulse signal in which the guard signal synchronizedwith the drive signal is superposed on a VGHO level.

Similarly to the fifth embodiment, the first positive polarityamplifiers 254 in the source amplifier 118 corresponding to a selectedcommon electrode outputs the pulse signal according to the guard signalduring a touch detection period. In order to output a pulse signal, thepositive polarity amplifier 254 requires power (a power source) when asignal level is changed from a low level to a high level or from a highlevel to a low level. The positive polarity amplifier 254 does notrequire power while the pulse is maintained at a high level or a lowlevel, and thus is set to a high impedance state. Therefore, asillustrated in waveform (b) of FIG. 25, during a touch detection period,the first positive polarity amplifier 254 in the source amplifier 118corresponding to the selected common electrode 22 is driven by apositive voltage VSP when the pulse is risen. Subsequently, the firstpositive polarity amplifier 254 is set to a high impedance state andthen driven by a ground level when the pulse is fallen. A high impedancestate may be achieved by turning off the power source of the positivepolarity amplifier 254 or, alternatively, by turning off a switch whichis connected to the output of the positive polarity amplifier 254.

In the sixth embodiment, similarly to the fifth embodiment, the guardsignal output from the source amplifier 118 (the positive polarityamplifier 254) is added to the drive signal Tx supplied to a selectedcommon electrode during a touch detection period. Therefore, the drivesignal Tx in a display panel is improved in slew rate, and the touchdetection is improved in accuracy. Furthermore, in the sixth embodiment,the positive polarity amplifier 254 is not kept driven during a touchdetection period, but is brought into a high impedance state when thepulse is maintained at a high level or a low level. Therefore, even if adrive signal supply source is a TSVCOM terminal alone, settlingcharacteristic will not be deteriorated. In addition, electric powerconsumption is reduced.

Seventh Embodiment

FIG. 26 is a block diagram indicative of a seventh embodiment concerninga self sensing type touch panel.

The first to the fifth embodiments are also applicable to a self sensingsystem. In the first to the fifth embodiments, common electrodes havinga long and narrow shape along a pixel column direction (Y axis) arearranged along a pixel row direction (X axis), as illustrated in FIG. 4.The seventh embodiment concerns a shape modification made to everycommon electrode in a self sensing system touch panel.

In the touch panel illustrated in FIG. 26, the common electrodes 22 arearranged in the shape of a two dimensional array. The output signal fromeach of the common electrodes 22 is used as a coordinate of a touchposition. One common electrode may be provided for every pixel or forevery some pixels. If one common electrode is provided for every somepixels, it may be provided for every some pixels arranged in a twodimensional array. Any shape may be applicable to a common electrode aslong as the common electrode can cover corresponding pixels.Furthermore, the common electrodes do not need to align vertically orhorizontally. The common electrode driver 126, the source amplifier 118,and the panel control signal generator 124 are driven during a touchdetection period similarly to the above mentioned embodiments. The selfsensing touch panel, as illustrated in FIG. 26, also makes it possibleto prevent any parasitic capacitance generated between a commonelectrode and a wiring from affecting any drive signals supplied to therespective common electrodes for touch detection.

Eighth Embodiment

A modification commonly applicable to all the embodiments mentionedabove will be explained as an eighth embodiment. FIG. 27 illustrates aportion of the panel control signal generator 124 relating to a guarddrive of a gate line according to the eighth embodiment. A voltageterminal 308 is added to the panel control signal generator 124 of thefirst embodiment illustrated in FIG. 13. The booster circuit 170 boostsup the positive external input power VSP (for example, +5.5V) twice. Theboosted voltage VGH (for example, +11.0V) is supplied to both the LDOregulator 172 and a first terminal of a selector 312. The selector 312has a second terminal in a high impedance state. The selector 312selects the first terminal during a display period, and selects thesecond terminal during a touch detection period. An output of theselector 312 is connected to the voltage terminal 308.

In short, the eighth embodiment may be obtained by adding to theflexible printed circuit board 28 illustrated in FIG. 13 a couplingcapacitor 316 connected between the voltage terminal 308 and the guardterminal 166.

The guard drive of the gate line by the panel control signal generator124 of FIG. 27 will be explained with reference to the timing chart ofFIG. 28. In FIG. 28, waveform (a) illustrates a state of the selector178 (the state is the same as waveform (a) of FIG. 14), waveform (b)illustrates a state of the guard terminal 166 (the state is the same aswaveform (b) of FIG. 14), waveform (c) illustrates a state of each ofthe selectors 174, 184, and 312 (the state is the same as the state ofeach of the selectors 174 and 184 in waveform (c) of FIG. 14), andwaveform (e) illustrates a state of the positive voltage terminal 162(the state is the same as waveform (d) of FIG. 14). The selector 312selects the first terminal during a display period, so that the terminal308 outputs a voltage of VGH as illustrated in waveform (d) of FIG. 28.The selector 174 selects the first terminal during a display period, sothat the terminal 162 outputs a voltage of VGHO as illustrated inwaveform (e) of FIG. 28. The selector 178 is connected to the disablingside during a display period, so that the terminal 166 is grounded.Therefore, the coupling capacitor 316 is charged with the voltage VGHduring a display period.

When the display period is changed to a touch detection period, theselector 178 will switch to the enabling side. The guard terminal 166outputs a pulsed guard signal, as illustrated in waveform (b) of FIG.28. The guard signal has amplitude of VHI. When the display period ischanged to the touch detection period, the selector 312 will switch tothe second terminal (high impedance). The guard signal output from theguard terminal 166 is supplied to the voltage terminal 308 through thecoupling capacitor 316. The capacitance of the coupling capacitor 316 isdetermined such that the current leakage from the coupling capacitor 316can be disregarded and the charges of the coupling capacitor 316 may bekept during a touch detection period. Therefore, as illustrated inwaveform (d) of FIG. 28, the voltage terminal 308 outputs a voltage inwhich the guard signal is superposed on the voltage VGH. Although notillustrated, the terminal 308 is also connected to the pixel array 18,and the power VGH is used as various kinds of electric power. Therefore,when the gate line 46, the source line 44, the control signal line ofthe RGB select switch 104, etc., are subjected to the guard drive, theinfluence of parasitic capacitance may also appear in the pixel array 18connected to the terminal 308 and the internal wirings of the touchpanel 20. However, during a touch detection period, the voltage of theterminal 308 becomes a voltage in which the guard signal is superposedon VGH (a guard drive is performed). It is considered that the voltageVGH is also subjected to the guard drive. Accordingly, the influence ofparasitic capacitance will not be exerted on the internal wirings.

Similarly to the first embodiment, when a display period is switched toa touch detection period, the selector 162 is switched to the secondterminal (high impedance). The guard signal output from the guardterminal 166 is applied through the coupling capacitor 144 to thepositive voltage terminal 162. The voltage of the positive voltageterminal 162 is a signal in which the guard signal is superposed onVGHO, as illustrated in waveform (e) of FIG. 28.

When the guard signal is superposed on the positive voltage terminal 162in the structure of FIG. 13 which does not have the coupling capacitor316, the positive voltage terminal 162 may have to be higher than thehigh voltage VGH depending on guard signal amplitude or VGH/VGHO settingvoltage. The difference between the voltage VGH and voltage VGHO needsto be greater than the guard signal amplitude VHI. However, guard signalamplitude is small in a self sensing system. A problem may not occureven in the structure of FIG. 13.

In the eighth embodiment, the guard signal is superposed on the voltageof the terminal 308 by the coupling capacitor 316. The voltage VGHO andthe voltage VGH is subjected to the guard drive. The difference betweenthe voltage VGH and the voltage VGHO is greater than the guard signalamplitude VHI. The gate line is stably subjected to the guard drive.

Overview of Embodiments

The embodiments include the following configurations.

(1) A display device includes:

-   -   a pixel array 18 including a plurality of pixels 40 arranged in        rows and columns;    -   common electrodes 22 over the pixel array 18 for capacitance        type touch detection;    -   a common electrode driver 126 configured to supply a direct        current voltage for display to the common electrodes 22 during a        display period and a drive signal Tx for touch detection to the        common electrodes 22 during a touch detection period;    -   source lines 44 connected to the columns of the pixels 40 in the        pixel array 18;    -   a source amplifier 118 configured to supply an image signal to        the source lines 44;    -   gate lines 46 connected to the rows of the pixels 40 in the        pixel array 18;    -   a gate driver 102 configured to successively supply a scanning        signal to the respective gate lines 46 during a display period,        and supply a guard signal in the same phase as the drive signal        to the gate lines 46 during a touch detection period; and    -   switches 148 connected between the source lines 44 and the        common electrodes 22 and configured to connect the source lines        44 and the common electrodes 22 during a touch detection period.

According to this display device, the source lines 44 and the commonelectrodes 22 are connected to each other by the switches 148 during atouch detection period. The drive signal Tx flowing through the commonelectrodes 22 also flow through the source lines 44. Therefore,parasitic capacitance will never occur between the source lines 44 andthe common electrodes 22. Moreover, the drive signals Tx flowing throughthe common electrodes 22 also flow through the gate lines 46 during atouch detection period. Therefore, parasitic capacitance will neveroccur between the gate lines 46 and the common electrodes 22. Accuracyof touch detection is prevented from being deteriorated by parasiticcapacitance and the common electrodes are driven by a desired waveformwith the use of the drive signals Tx.

(2) In the display device of (1), the common electrodes 22 include avertical COM type common electrode, and are parallel to signal lines 44.

(3) In the display device of (1), the common electrodes 22 include ahorizontal COM type common electrode, and cross signal lines 44.

(4) The display device of (1) has detecting electrodes 24 intersectingthe common electrodes 22. The drive signal Tx is supplied to the commonelectrodes 22, and touch detection is performed by a mutual sensingsystem based on the detected potential detected by the detectingelectrodes 24.

(5) In the display device of (1), the drive signal is supplied to thecommon electrodes 22, and touch detection is performed by a self sensingsystem based on change of the capacity of the common electrodes 22.

(6) In the display device of (1), touch detection periods are within oneframe period, and a touch detection period is between a display periodand a next display period. Constant direct current voltage is suppliedto the common electrodes during a display period. The driving pulse issequentially supplied to the common electrodes for touch detectionoperation.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be brought into practice in a variety of other forms; furthermore,various omissions, substitutions and changes may be made in theembodiments described herein without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A display device comprising: pixels arranged inrows and columns; common electrodes overlapping the pixels; gate linesextending in a first direction and arranged in a second direction, eachof the gate lines connected to pixels in each row; source linesextending in the second direction and arranged in the first direction,each of the source lines connected to pixels in each column; sourceamplifiers configured to supply an image signal to the source lines; anda gate drive circuit configured to supply at least one first pulse tothe gate lines, wherein the gate drive circuit comprises: a gate driverwith a high voltage terminal and a low voltage terminal; a firstterminal configured to receive a first voltage; a second terminalconfigured to receive a second voltage lower than the first voltage; apulse generator configured to output the at least one first pulse, andan output terminal of the pulse generator connected to an outputterminal of the gate driver; a first switch connected between the highvoltage terminal and the first terminal; a second switch connectedbetween the low voltage terminal and the second terminal; a third switchcoupled between the high voltage terminal and the output terminal of thegate driver; and a fourth switch coupled between the low voltageterminal and the output terminal of the gate driver.
 2. The displaydevice of claim 1, wherein: a first capacitor is connected between theoutput terminal of the pulse generator and the high voltage terminal;and a second capacitor is connected between the output terminal of thepulse generator and the low voltage terminal.
 3. The display device ofclaim 2, wherein: the at least one first pulse is not supplied to theoutput terminal of the gate driver, the first switch and the secondswitch are conductive, and the first voltage and the second voltage aresupplied to the gate driver during a display period; and the firstswitch and the second switch are not conductive and the at least onefirst pulse is supplied to the gate driver during a touch detectionperiod.
 4. The display device of claim 3, further comprising: a commonelectrode driver configured to supply at least one second pulse to thecommon electrodes during the touch detection period, and wherein the atleast one second pulse is synchronous with the at least one first pulse;and an amplitude of the at least one second pulse is substantially equalto an amplitude of the at least one first pulse.
 5. The display deviceof claim 4, wherein: the source lines are connected to the commonelectrodes and the common electrodes are driven by the at least onesecond pulse through the source lines during the touch detection period.6. The display device of claim 5, wherein: selectors are connectedbetween the source amplifiers and the source lines; the image signal issupplied to the pixels through the selectors during the display period;the at least one second pulse signal is supplied to the commonelectrodes through the selectors and the source lines during the touchdetection period; the selectors are selected by selection controlsignals which are synchronous with the at least one second pulse signal;and an amplitude of the selection control signal is substantially equalto an amplitude of the at least one second pulse signal.
 7. The displaydevice of claim 4, wherein the common electrode drives is configured tosimultaneously supply the at least one second pulse to the commonelectrodes during the touch detection period in order to executeself-sensing touch detection based on capacitance of the commonelectrodes.
 8. The display device of claim 4, wherein each of the sourceamplifiers comprises a positive polarity amplifier and a negativepolarity amplifier, and the positive polarity amplifier is configured tooutput a signal in the same phase as the at least one second pulseduring the touch detection period.
 9. The display device of claim 4,further comprising detection electrodes crossing the common electrodes,wherein: the at least one second pulse is successively supplied to thecommon electrodes in order to execute a mutual sensing touch detectionbased on a detected potential of the detection electrodes during thetouch detection period; and a drive signal is supplied to the commonelectrodes during the touch detection period.
 10. The display device ofclaim 4, wherein: the common electrodes are two dimensionally arrayed;and the at least one second pulse is successively supplied to the commonelectrodes in order to execute self-sensing touch detection based oncapacitance of the common electrodes.
 11. The display device of claim 4,wherein the gate drive circuit comprises a voltage boosting circuitconfigured to boost an external power source voltage to order togenerate the at least one first pulse, and, wherein the gate drivecircuit is configured to successively supply a scanning signal based onthe first voltage to the gate lines during the display period, andsupply a signal, and wherein a signal in the same phase as the at leastone second pulse is superposed on the first voltage to the gate linesduring the touch detection period.
 12. The display drive of claim 3,wherein the source amplifiers are driven by a power source when a signallevel changes from a low level to a high level or from a high level to alow level during the touch detection period and is set to a highimpedance state when the signal level is kept at a low level or a highlevel during the touch detection period.
 13. The display device of claim2, wherein: a first booster is connected between the first terminal andthe high voltage terminal; and a second booster is connected between thesecond terminal and the low voltage terminal.
 14. The display device ofclaim 1, wherein: each of the pixels comprises sub pixels of differentcolors; and the image signal comprises a time division multiplex signalcomprising sub pixel signals of the different colors.